Categorization is often a very short distance away from censorship, if it is made in terms of value judgements such as "toxic".

> Use all the fancy recommendation algorithms to let the scholars scholar, and the trolls happily troll with other trolls.

The problem is that this algorithm has nothing to do with scholarly value of the uterring, while it will be widely perceived as an objective judgement on such value. If you call somebody a "troll", it's just your opinion, if you use blackbox algorithm to do it, it's kinda objective truth. That's the worrying part - because there's no evidence blackbox algorithm is better, and actually so far plenty of evidence it's worse.